Dermoscopy is the term used to describe methods of imaging skin lesions. Skin is the largest organ in the body and it is the most easily accessible organ for external optical imaging. For early detection of cancers, it is important that the skin be medically examined for lesions.
With over forty (40%) percent of the cancers occurring on the skin (American Cancer Society Statistics 2001, Perelman 1995), and incidence of skin cancer increasing each year, tools and methods of imaging skin lesions are becoming increasingly important. Most of the cancers detected on the skin are Basal Cell Carcinoma (BCC) and Squamous Cell Carcinoma (SSC), which are differentiated from melanoma, a more deadly form of skin cancer. The early detection of skin cancer allows for inexpensive treatment before the cancer causes more severe medical conditions. Thus, there is a great need in the art for simple inexpensive instruments that allow for the early screening for skin cancer.
Because skin is partially translucent, dermoscopy utilizes tools for visualization of the pigmentation of the skin below the surface. In this regard, when attempting to visualize the deeper structure of the skin, it is important to reduce the reflection of light from the skin that may obscure the underlying structures. Methods used to reduce the surface reflection from the skin are referred to as epiluminescence imaging. There are three known methods for epiluminescence imaging of the skin, oil-immersion, cross-polarization, and side-transillumination. Oil-immersion and cross-polarization methods have been extensively validated for early skin cancer detection while side transillumination methods are currently undergoing study and clinical validation.
Oil-immersion devices are generally referred to as Dermatoscopes. Dermatoscopes permit increased visualization of subsurface pigmentation by using a magnification device in association with a light source. In operation, oil is placed between the skin and a glass faceplate. The placement of oil and a glass interface between the eye and the surface of the skin reduces the reflected light from the skin, resulting in deeper visualization of the underlying skin structure.
While oil-immersion has proved to be an excellent method of epiluminescence imaging of the skin, demonstrating improved sensitivity for melanoma detection, it is messy and time consuming for the physician. As a result, the Dermatoscope is used mostly by physicians that specialize in pigmented lesions and for evaluation of suspicious lesions that cannot be diagnosed visually. Also, the oil-immersion of the Dermatoscope has been found to be less effective for BCC and SCC imaging. The pressure created by the compression of the glass faceplate causes blanching of blood vessels in the skin resulting in reduced capability of the Dermatoscope for imaging the telangiectesia that is often associated with BCC or other malignent lesions.
Cross-polarization or orthogonal polarization is another method of reducing the reflection of the light from the surface of the skin to aid in the medical examination of the skin. Light emanating from a light source is first linearly polarized, so that the orientation of the light falling on the skin surface is in the same plane of polarization. As the light enters the skin, its polarization angle changes such that the light is reflected from a deeper structure. However, the light reflected from the surface of the skin is still polarized in the same plane as the incident light. By including a second polarizer in the path of the reflected light from the skin, a selective filtering of light can be achieved.
Most of the light directed to the skin's surface is reflected, as the refractive index of skin is higher than that of air. The reflection of light, off of the skin, is analogous to the reflection of light off of the surface of water. Accordingly, the information received by the eye carries mostly information about the contour of the skin surface rather than the deeper structures. Remaining light enters the skin and is absorbed or is reflected back in a scattered fashion. By polarizing the incident light with a second polarizer, the specular component of the reflected light is blocked by the viewing polarizer, thus producing an enhanced view below the skin surface. Accordingly, inflammation, color, pigmentation, hair follicles, blood vessels and other structures may be viewed.
When the incident light and the second polarizer are parallel, the surface topography and properties of the skin are highlighted and enhanced. In this regard, if the polarizer in the path of the light from the skin to the eye is polarized in the same orientation of the incident light, only the light from its polarization angle will be allowed to pass through the lens. Cross-polarization imaging of the body was originally described by R. R. Anderson (“Polarized light examination and photography of the skin.” Archives Dermatology 1991; 127; 1000–1005). Later, Binder introduced the MoleMax manufactured by Derma Instruments (Vienna, Austria) for the examination and mapping of pigmented lesions. Binder further developed the no-oil cross-polarization epiluminescence method. MoleMax, however, while validating clinically the improved diagnosis and accuracy without the use of oil, still used a glass faceplate and video imaging system to execute skin examinations.
In light of many of the difficulties associated with prior dermoscopy systems, simple and cost-effective diagnostic systems remained unavailable for general dermatologists to use on a routine clinical basis. Dermoscopy, until recently, remained generally a research tool utilized in special clinical cases. More recently, however, a substantial advancement in skin cancer detection occurred through a simple device identified as DermLite®, manufactured and marketed by 3Gen, LLC, Monarch Beach, Calif. With the low cost and ease of use of the DermLite® Device, screening for cancer by dermatologists, in routine clinical examination of skin disease, has become a reality. The DermLite® device uses cross-polarization epiluminescence imaging through use of white light emitting diodes (LEDs), a high magnification lens (10×), and a lithium ion battery contained in a small lightweight device.
In the DermLite® device, a window is incorporated into a compact housing, and a plurality of white light LEDs encircle a magnifying lens. The DermLite® device incorporates cross-polarization filters that reduce the reflection of light from the surface of the skin and permits visualization of the deeper skin structures. Light from eight (8) LEDs is polarized linearly by a polarizer, which is annular in shape and located in front of the LEDs. The imaging viewed through the magnifying lens is also linearly polarized by using a polarizer that is located in front of the lens. The LEDs have a narrow beam angle that concentrates the light into a small area, pointing the incident light to the center to increase the brightness of the area being viewed. Thus, light from the LEDs passes through the polarizer which enters the skin and reflects back through the viewing polarizer to create cross-polarization allowing examination to look deeper within the skin structure. Although, the DermLite® product has been recognized as a major advancement in the art of routing clinical diagnosis and analysis of skin cancer lesions, DermLite® device does not provide a mechanism for enabling the user to additionally view parallel-polarized light, or a combination of cross-polarized light and parallel-polarized light. The DermLite® Platinum™ product, also manufactured by 3Gen, LLC., was developed to provide variable polarization. In the Dermlite® Platinum™, a rotating dial achieves variable polarization. Rotation of the polarizer to a cross-polarization cancels out the surface reflection for an in-depth look at the deeper pigmentation in lesion structure. Rotation to parallel polarization allows a clear view of the skin surface. The DermLite® Platinum™ product requires manual manipulation of the dial which may cause user to lose the viewing spot, or otherwise interfere with examination. Further, DermLite®Platinum™ does not provide a user the ability to view the skin with an instantaneous switch over from cross-polarization to parallel polarization.
The DermLite®Pro DP-R™ also manufactured by 3gen, LLC, was developed to provide instant, button activated, polarization control. Embodiments of the DermLite® Pro DP-R™ are disclosed in U.S. patent application Ser. No. 10/384,110 filed Mar. 7, 2003, the substance of which is incorporated by reference. Variable mode polarization is provided by a toggle switch that allows the viewer to view the surface of the skin using a polarizing mode, and a switch mode, and a switch creates a cross-polarization which cancels out surface reflection for a view of the deeper pigmentation and structures of the skin.
While existing devices have been proven for effectiveness in detecting melanomas, non-melanoma skin cancers (NMSC) such as BCC and SSC have little or no melanin and therefore are very hard to detect by classical dermoscopy methods. Detection of NMSC is usually carried out by visually examining the suspected reddish areas of skin eruptions with a magnifying lens. Early NMSC are usually detected by looking for the presence of abnormal blood vessels, which are best seen with an epiluminescence device that does not use a glass faceplate and oil. The presence of a glass faceplate and oil blanches the blood vessels and makes it difficult to see the increased vascularity. In addition, NMSC excision boundaries are very difficult to estimate without the information about the subsurface extension of the lesion. Kumar et al (2002) [inset cite] examined 757 BCC that were excised in a British hospital and found positive margins in 3.1% to 7.5% of the excisions, depending on the location of the lesion. Another study by Hallock et al (2001) [Hallock G G, Lutz D A, 2001, A Prospective Study of the Accuracy of the Surgeon's Diagnosis and Significance of Positive Margins in Non-Melanoma Skin Cancers. Plast Reconstr Surg 107:942–7] examined the incidence of positive margins in excised lesions from a private clinic. They found that 20% of all the excisions were malignant (98% were NMSC) and that within the malignant group, 15.7% of the NMSC had positive margins. In this study, 80% of all the excisions were not malignant. Both studies show a significant percentage of excisions with positive margins using present methods.
The presence of positive margins could contribute in part to the recurrence of NMSC. In Australia, where the incidence of BCC and SCC is extremely high (3% as reported by Diepgen et al (2002)), recurrence of NMSC, as reported in a three (3) year study by Czarnecki et al (1996), is 8%. The incidence of multiple NMSC in Australian population was found to be 38.5%, as published in a large study by Raasch et al (2002). And, in a 10 years study by Czarnecki et al (2002), the incidence of second skin cancer occurred in 67.8% of the study population with very high odds for malignant melanoma in the NMSC patients. Incomplete excision can result in recurrence of disease at the same site. And, once the skin lesion becomes larger and is located on the face, normal excisions cannot be performed. Instead, a costly procedure called Mohs Microsurgery (MMS) needs to be performed to remove only the minimum amount of normal tissue. Welch et al (1996) studied the incidence of MMS in 5193 NMSC over a five years period. They found that 32.7% of the NMSC had MMS surgery during the five-year period.
NMSC are characterized by reddish fleshy (nodular) or flat (sclerosing) areas on the skin. These skin lesions usually grow from a pinpoint-sized object, that looks like a pimple, to as large as several mm in size. NMSC are usually found on the head and the neck areas. Ceylan et al (2003) [Ceylan C., Ozturk G, Alpers S., 2003 Non-melanoma Skin Cancers Between the Years of 1990 and 1999 in Izmir, Turkey: Demographic and Clinicopathological Charactoristics. J. Dermaol 30:123–31] showed, in a Turkish population, that 46.6% of the NMSC were located on the face, and that 78.4% of the lesions were between 11 and 20 mm in size at the time of diagnosis.
The visual features that make NMSC different from surrounding normal skin are the abnormal blood vessels and increased vascularity of the lesion. Bedlow et al (2003) [Bedlow A J, Stanton A W, Cliff S., Mortimer P S. Basal Cell Carcinoma and In-vivo Model of Human Tumor Microcirculation? Exp Dermatol 1999, 8:222–6], using video capillaroscopy for the examination of blood vessels in situ, showed that the superficial blood vessels in the BCC are larger and longer than normal blood vessels. They computed the ratio of BCC vessels to normal vessels and found that the area of the BCC vessel was 4.9 times larger and the length was 5.9 times longer than for normal vessels. Weninger et al (1997) [Weninger W, Rendl M, Pammer J, Grin W, et al 1997. Differences in Tumor Microvessel Density Between Squamous Cell Carcinomas and Basal Cell Carcinomas May Relate to Their Different Biological Behavior. J Cutan Pathol 24:364–9] found that SCC had larger vascularity than normal tissue in a study that examined microvessel density (MVD) in excised tissue. Stanton et al (2003) [Stanton A W, Drysdale S B, Patel R, Mellor R H et al. 2003. Expansion of Microvascular Bed and Increased Solute Flux in Human Basal Cell Carcinoma In-Vivo, Measured by Fluorescein Video Angiography. Cancer Res 63:3969–79] used laser Doppler flow and video microscopy with injections of fluorescein to study BCC in vivo. They found increased vasculature and blood flow in BCC. Increased number of blood vessels and larger sized blood vessels means a larger blood volume, which is usually associated with increased blood flow in malignant lesions. Accordingly, finding an inexpensive means to view and analyze these features is therefore important in the field.
Recent discoveries in optical fluorescence imaging have identified several molecules having fluorescence properties that are useful in medicine and in particular, dermatology. Simple applications such as delta-aminolaevulinic acid (ALA) applied topically have been found to enhance the visualization of basal cell cancer from normal tissue, when illuminated with UV/Blue light. Fluorescein is another fluorescent compound that has been in clinical use in opthamology for several years and has great potential for use in dermatological applications. Indocyanine green (ICG), Methylene Blue, and ethyl nile blue are contrast agents that are used to increase light absorption in blood vessels. There are several FDA approved optical fluorescence tracers already approved for clinical use, and several more new probes may be applicable in the future. However, the use of fluorescence imaging of the skin has been illusive for clinical dermatologist because of the complexity and costs of the associated equipment.
In current applications, such as in the application of ALA topically to a basal cell carcinoma to a BCC, conventional white light visual images of the BCC are displayed next to the fluorescence excited images of ALA in the BCC. The ALA is taken up by the active areas of cancer, converted to porphyrin IX, and fluoresces when exposed to UV/Blue light. It becomes apparent that the fluorescent areas of the BCC may not coincide with the anatomical features of the BCC as shown in white light. Currently the side-by-side comparison is only available by taking two separate images and co-registering these images later in the computer.
Thus, there is a great need in the art for a device that will allow clinical viewing of skin lesions which provides on demand switching that can toggle back and forth from a white light to a colored or UV light in order to contrast and compare images. Further there is a great need in the art for a device to allow the clinical viewing of skin lesions that provides on demand switching that can toggle between from lights of differing wavelengths or colors. Further there is a great need in the art to allow the on-demand comparison images of the skin illuminated by differing wavelengths viewed in combination with cross and parallel polarization.